Microfiltration Membrane Module Research Articles

Evaluation of a submerged membrane vis-LED photoreactor (sMPR) for carbamazepine degradation and TiO2 separation

A hybrid submerged membrane photoreactor (sMPR) combining a photoreactor irradiated with visible-light-emitting diode (vis-LED) and a submerged hollow fiber PVDF microfiltration (MF) membrane module was investigated in a continuous flow-through mode. A global carbamazepine (CBZ) photocatalytic degradation rate constant at steady state was achieved at (19.4±2.35)×10−3min−1 with hydraulic residence times (HRTs) in the range of 30–300min using a visible-light responsive C–N–S tridoped TiO2 (T0.05-450). An alkaline pH condition was favorable for the CBZ photocatalytic degradation. The inhibitory effects of inorganic anions on the CBZ photocatalytic degradation followed the order of silica>phosphate>nitrate>bicarbonate>sulfate>chloride. The net effect of humic acid (HA) on the CBZ degradation depended on the three competitive phenomena: (i) HA as an electron shuttle promoting the generation of O2- while reducing the electron–hole recombination, (ii) HA competing with CBZ for the active sites of the photocatalyst, and (iii) HA contributing to the light attenuation in the photoreactor. The MF membrane realized effective separation of T0.05-450 as the turbidity of permeate water was<0.1 NTU. A steady-state transmembrane pressure (TMP) was achieved after its increase in the first 2h due to the deposition of TiO2 cake layer on the membrane surface. NaOH (pH=11) and 0.5mM EDTA (pH=11) solutions were efficient for cleaning the membrane surface fouled by HA. For the long-term operation of the sMPR system, the reduction of CBZ photocatalytic degradation efficiency could be attributed to the decrease of the photocatalyst dosage in the suspension, and the aggregation and deactivation of TiO2 particles during the prolonged operation.

Membrane vis-LED photoreactor for simultaneous penicillin G degradation and TiO2 separation

The hybrid membrane photoreactor (MPR) combining a photoreactor irradiated with visible-light-emitting diode (vis-LED) and a cross-flow microfiltration (MF) membrane module was investigated in both closed-loop and continuous flow-through modes for the simultaneous degradation of penicillin G (PG) and separation of visible-light responsive TiO2 particles, namely C-sensitized-N-doped TiO2 (T300) and C–N–S tridoped TiO2 (T0.05-450). The turbidity of permeate water was <0.2 NTU for both T300 and T0.05-450 suspensions in the MPR system operated at different transmembrane pressures (TMPs) and cross-flow velocities (CFVs), indicating effective separation of TiO2 particles by the MF membrane. The operations at a higher TMP or lower CFV were more prone to induce TiO2 deposition on the membrane surface without backwashing, which resulted in the membrane fouling, the loss of TiO2 from the photoreactor and the decrease of PG photocatalytic degradation efficiency. 75% and 84% of PG were degraded in the closed-loop MPR without backwashing operated at 10 kPa and 0.15 m s−1 after 4 h of vis-LED irradiation using 1.0 g L−1 of T300 and T0.05-450, respectively. With backwashing of the membrane, the PG photocatalytic degradation efficiencies in the closed-loop MPR could be significantly enhanced to achieve 93% and 95% using 1.0 g L−1 of T300 and T0.05-450, respectively, which were almost comparable to those achieved in the batch photoreactor. Due to its shorter hydraulic residence time in the photoreactor, the PG degradation efficiency in the continuous flow-through MPR with backwashing was lower than that achieved in the closed-loop MPR.

The use of a submerged membrane batch reactor (S.M.B.R) for co-treatment of landfill leachates and domestic wastewater

Abstract The aims of this work were the examination of the treatment potential of landfill leachates domestic wastewater mixtures by a pilot scale membrane bioreactor system using a submerged plate and frame microfiltration (MF) membrane module and the investigation of the optimum operation conditions for the achievement of maximum COD and total nitrogen removal rates. The bioreactor was inoculated by 60 l of activated sludge and operated at an MLSS content reaching up to 25,000 mg/l; increased COD removal efficiencies were observed reaching up to 98%. High ammonium nitrogen removal efficiencies were achieved reaching up to 99% at extended operation times associated to long SRTs, resulting in effluent concentrations of about 1 mg/l; however, total nitrogen content of effluents was high, about 160 ± 50 mg/l, due to reduced denitrification capacity of the system.

Direct production of l (+) lactic acid in a continuous and fully membrane-integrated hybrid reactor system under non-neutralizing conditions

Experimental investigations were carried out on continuous and direct production of l (+) lactic acid by fermentation of sugarcane juice in a novel two stage membrane-integrated fermentor under non-neutralizing conditions. Novelty of the integrated system lies in high degree of purity, yield and productivity of lactic acid from a relatively cheap and renewable carbon source in a very compact, flexible yet eco-friendly plant. Integration of cross flow microfiltration and nanofiltration membrane modules in two stages with the fermentor helped achieve reasonably high purity, productivity and yield by continuous recycling of cells and unconverted sugars. The system could be operated at steady state for a constant fermentor capacity and also at different set flux values ranging from 63 l m −2 h −1 to 76 l m −2 h −1. Cross flow microfiltration membrane modules ensured almost complete separation and recycle of cells without much fouling problem whereas composite nanofiltration membrane module helped achieve 96% recovery and recycle of unconverted sugars along with high degree of purity. When operated at a dilution rate of 0.15 h −1, the yield and volumetric productivity of l (+) lactic acid were 0.96 g g −1 and 12.40 g l −1 h −1 respectively. Volumetric productivity could be increased further to 13.4 g l −1 h −1 with increase of dilution rate to 0.18 h −1. Flat sheet cross flow modular design permitted continuous production of lactic acid in a highly flexible, largely fouling-free and environmentally benign plant as direct lactic acid was obtained instead of lactate salts of a conventional process.

Continuous d-lactic acid production by a novelthermotolerant Lactobacillus delbrueckii subsp. lactis QU 41

We isolated and characterized a D-lactic acid-producing lactic acid bacterium (D-LAB), identified as Lactobacillus delbrueckii subsp. lactis QU 41. When compared to Lactobacillus coryniformis subsp. torquens JCM 1166 (T) and L. delbrueckii subsp. lactis JCM 1248 (T), which are also known as D-LAB, the QU 41 strain exhibited a high thermotolerance and produced D-lactic acid at temperatures of 50 °C and higher. In order to optimize the culture conditions of the QU 41 strain, we examined the effects of pH control, temperature, neutralizing reagent, and initial glucose concentration on D-lactic acid production in batch cultures. It was found that the optimal production of 20.1 g/l D-lactic acid was acquired with high optical purity (>99.9% of D-lactic acid) in a pH 6.0-controlled batch culture, by adding ammonium hydroxide as a neutralizing reagent, at 43 °C in MRS medium containing 20 g/l glucose. As a result of product inhibition and low cell density, continuous cultures were investigated using a microfiltration membrane module to recycle flow-through cells in order to improve D-lactic acid productivity. At a dilution rate of 0.87 h(-1), the high cell density continuous culture exhibited the highest D-lactic acid productivity of 18.0 g/l/h with a high yield (ca. 1.0 g/g consumed glucose) and a low residual glucose (<0.1 g/l) in comparison with systems published to date.

MBR plants in China use Sumitomo's Poreflon MF modules

Sumitomo Electric Fine Polymer Inc (SFP) reports that its microfiltration (MF) membrane module, which is designed for use in membrane bioreactors (MBR), is being used for the first time in industrial wastewater treatment plants in China.

MBR module design and operation

Membrane Bioreactor (MBR) technology is widely accepted today for wastewater treatment providing superior effluent quality, opportunities for water reuse, smaller footprint, and better process control. In the following paper, the development and application of hollow fibre submerged membrane modules in Membrane Bioreactors will be discussed. Early MBR systems used tubular cross flow micro-filtration (MF) or ultra-filtration (UF) membrane modules but the huge energy demand for cross flow technology limited it to heavily polluted niche applications. In the late 80’s the development of submerged membrane technology reduced the energy consumption by using aeration to induce a cross flow and withdrawing purified water by slight vacuum allowing the adoption of MBR technology to more conventional applications. Based upon the m 2 of membrane area sold/used worldwide, hollow fibre membrane technology is today the most successful submerged MBR technology.

A comparative study of tertiary membrane filtration of industrial wastewater treated in a granular and a flocculent sludge SBR

Membrane fouling has been identified by many researchers as an inconvenience for the industrial application of membranes in wastewater treatment plants. Membrane fouling decreases permeability and therefore permeates flow, increasing costs. Although fouling is the result of complex phenomena not completely known, it can be said that fouling takes place by the presence of three different kinds of compounds in the water: suspended solids, colloids and solutes. In this sense, the characteristics of the suspended solid aggregates might be an important aspect in order to diminish the impact of suspended solids on membrane fouling. The main objective of this study was to compare the operation of two similar tertiary membrane filtration units treating the effluent of two different SBRs, respectively: A granular sludge SBR (GSBR) and a membrane flocculent sludge SBR system, at laboratory scale. Two PVDF microfiltration membrane modules were used for tertiary filtration of the effluent treated in the SBRs. Both reactors were used for treating the wastewater generated in a factory of the fish freezing sector. COD of the wastewater was between 700 and 1100 mg/L, total nitrogen concentration was between 110 and 180 mg N/L and total phosphorus ranged around 110 mg P/L. The chemical characteristics of both permeates were similar. Moreover, the presence of either granules or flocs in the tertiary membrane filtration systems did not have an appreciable impact on the membrane filtration. Nevertheless, it was observed that the operation of the membrane on the flocculent system tends to be more instable, showing a major tendency to achieve critical flux.

Mechanism investigation of virus removal in a membrane bioreactor

Virus removal in a membrane bioreactor (MBR) by gravity drain was studied. Coliphage f2 (mean size of 25 nm), which is similar in size to human enteric pathogenic viruses, was selected as a model virus. Two microfiltration membrane modules with pore sizes of 0.22 μm and 0.1 μm were applied to investigate the effects of membrane pore size on the virus rejection. The MBR with these modules could reject virus in a range of 2.6–5.1 logs. The experimental results showed that the mechanisms of virus removal in the MBR involved rejection and inactivation. The virus rejection depended mainly on the dynamic layer on the membrane surface (not membrane itself) because virus rejection by the membrane modules with pore sizes of 0.1 μm and 0.22 μm were similar. The microbial activity and the aeration oxidation were the two important factors for the virus inactivation. It was found that the inactivation of coliphage f2 was much more rapidly in activated sludge mixed liquor than in clean water, and the effect of aeration was significant.

Continuous hydrogen production by anaerobic mixed microflora using a hollow-fiber microfiltration membrane bioreactor

A membrane bioreactor (MBR) fabricated by connecting a hollow-fiber microfiltration membrane module with a continuous flow stirred tank reactor (CSTR) was used to enhance H 2 production through high-dilution rate operations. Three different carbon substrates (glucose, sucrose, and fructose) were examined for their effectiveness in H 2 production with a mixed microflora. The results show that in CSTR operation, cell washout occurred at a hydraulic retention time (HRT) of 2–4 h. Using MBR could avoid cell washout, leading to a substantial increase in both H 2 production rate (HPR) and biomass concentration. The MBR system was very effective in retaining biomass within the reactor as the system can be stably operated at an extremely low HRT of 1 h with an optimal steady-state HPR of 1.48, 2.07, and 2.75 l/h/l, respectively, for using glucose, sucrose, and fructose as the sole carbon source. Meanwhile, despite operation at a high dilution rate (i.e., HRT = 1 h ), the H 2 yield (HY) could be maintained at a high level of 1.27, 1.39, and 1.36 mol H 2 / mol hexose, for glucose, sucrose, and fructose, respectively. Irrespective of the bioreactor mode (CSTR or MBR), the HPR tended to decrease in the order of fructose > sucrose > glucose . Thus, fructose seems to be the most efficient carbon substrate for H 2 production with the H 2 -producing mixed culture used in this work. Butyrate (HBu) and acetate (HAc) (especially, HBu) were the major soluble metabolites in all cases, contributing to 70–85% of total soluble microbial product (SMP). The HPR and HY could be estimated based on stoichiometric correlation between formation of soluble metabolites (i.e., HBu, HAc, and propionate) and H 2 production. The estimated values are in good agreement with the experimental results.

Selective Isolation and Purification of Genetically Modified Tat Protein by Stacked Affinity Membrane System

Recognition based separation using modified microfiltration membranes provides an efficient and cost-effective alternative to conventional column chromatography for the isolation and purification of a specific protein from mixture of proteins. Tat is a regulatory protein that is critical for HIV-1 replication and thus a potential candidate for vaccine and drug development. Tat can be genetically engineered to attach a biotin molecule, and then can be obtained in a complex mixture of proteins, known as bacterial lysate (BL). Tat (naturally biotinylated) accessibility in the bacterial lysate feed was influenced by the presence of RNAse, protein concentration and ionic strength. Enhanced accessibility translated to a marked increase in the overall product yield per pass. In this study, Tat has been separated and purified from BL using avidin-biotin interaction in a modified 4-stack microfiltration membrane module. It has been established by SDS-PAGE and Western Blot analysis that membrane based process recovered purer Tat in compared to conventional column chromatographic process. The critical factors involved in the process, mainly, the accessibility of the covalently immobilized avidin sites by the biotinylated protein and the associated fouling of the membranes due to the permeation of proteins, have also been studied. Tat protein produced via membrane separation yielded primarily monomeric forms of the oligopeptide sequence, where as, column chromatography produced predominately polymeric forms of Tat. These differences resulted in changes in the neurotoxicity and cellular uptake of the two preparations. This research has been supported by a NIH grant.

Evaluation of virus removal in MBR using coliphages T4

A membrane bioreactor (MBR) with gravity drain was tested for domestic wastewater for 65 days. Results showed that the effluent quality was excellent, and met with the reuse water standard of China (GB/T 18920–2002). Virus removal in the membrane separation process was investigated by employing coliphages T4 as a tracer. Two microfiltration membrane modules, with pore sizes of 0.22 and 0.1 μm, were used to investigate their effects on virus rejection at the transmembrane pressure of 8.5 kPa. It was found that 0.1 μm, membrane had complete rejection of virus, and 0.22 μm, membrane had significant rejection of virus. In the longterm operation of this MBR, no significant difference was observed between both pore sizes because the virus concentrations of the effluent in both cases were in the same order. Effluent virus concentration at steady state of MBR running was less than 2 PFU/mL. The removal ratios of coliphage T4 in MF processes were more than 105.5. The membrane surface deposits played an important role in the rejection of virus. The formation of cake clay on the membrane surface was the main cause of high rejection of coliphage T4 with MF of 0.22 μm.

Non-invasive visualization of the fouling of microfiltration membranes by ultrasonic time-domain reflectometry

An ultrasonic time-domain reflectometry (UTDR) technique has been applied to the non-invasive study of fouling in microfiltration (MF) membrane modules operating at 100 kPa. The experimental results show a good correspondence between the UTDR signal response from the membranes and the development of a fouling layer on the membrane surface. The ultrasonic technique could effectively detect fouling-layer initiation and growth on the membrane in real-time. For experiments conducted at different axial velocities, ranging from 1.83 to 23.0 cm/s ( Re from 65.4 to 811), a sequential mode fouling layer growth was observed. The UTDR technique was capable of distinguishing individual modes of growth. The data also suggest the formation of a second echo in the time domain at 100 kPa operating pressure. Therefore, the UTDR technique was used to quantify the thickness of a fouling layer. The non-invasive UTDR visualization of the fouling on the membrane surface was supported by “post-mortem” SEM analysis of the membrane surface. The UTDR technique can be more suitable for non-invasive visualization of the fouling in MF system.

Performance comparison of direct membrane separation and membrane bioreactor for domestic wastewater treatment and water reuse

Two pilot-scale wastewater treatment systems - direct membrane separation (DMS) and membrane bioreactor (MBR) systems - were designed and constructed in order to investigate the feasibility of membrane filtration technology for domestic wastewater treatment and water reuse. A submerged-type hollow-fiber microfiltration (HF-MF) membrane module with pore size of 0.1μm was employed to build each pilot system. The systems were tested using low- and high-strength domestic wastewaters and the system performance was continuously monitored for a long period to compare filtration characteristics and effluent quality in each system. The MBR system showed much better performance than the DMS system in terms of filtration characteristics and effluent quality. Even though the mixed-liquor suspended solid (MLSS) content in the MBR system was much higher than that in the DMS system, the MBR filtration resistance was much lower than the DMS filtration resistance. The DMS system was not able to remove dissolved organic matter, which seemed to be a major component of membrane fouling. The MBR effluent quality such as COD, BOD, TOC and T-N was more stable and better than the DMS. In the MBR process, the organic removal efficiency remained more than 95% regardless of fluctuation in influent qualities. The effluent quality of both systems was satisfying the legal standards for water reuse in Korea. Rejection of pathogenic microorganisms by membrane filtration was also investigated.

Fate of indigenous bacteriophage in a membrane bioreactor

Indigenous bacteriophage was isolated from a conventional sewage treatment plant treating a largely domestic wastewater. The isolated phage was T-even-like with a mean size of 200 nm and was used to indicate the viral removal efficiency achieved in a bench-scale membrane bioreactor (MBR). The MBR incorporated three flat microfiltration membrane modules which were polyethylene with a pore size of 0.4 μm. When treating settled domestic sewage, the MBR achieved an overall removal rate of phage of 2.3–5.9 log across the treatment process. The membrane alone demonstrated a poor phage removal efficiency, but removal efficiency increased as the filtration resistance was increased. It was proposed therefore, that the biofilm accumulating on the surface of the membrane made a major contribution to phage removal. The MBR demonstrated an almost complete removal of faecal coliforms and faecal streptococci (up to 7 log). By comparison a full-scale treatment plant treating the same settled sewage and incorporating tertiary treatment, achieved only up to 2 log removal of the same excreted phage and bacteria.

Viscosity effects on Dean vortex membrane microfiltration

AbstractThe influence of changing viscosity by adding polyethylene glycol (PEG) during microfiltration of silica suspensions in the presence and absence of Dean vortices was determined. A new microfiltration membrane module design containing helically wound hollow fibers (with Dean vortices) was compared with a standard commercial cross‐flow module (without Dean vortices) containing linear hollow fibers during filtration of poly(ethylene) glycol solutions and silica suspensions. The influence of solution viscosity on permeation flux behavior was evident through two separate effects. First, increased viscosity effected the formation and stability of vortices and, hence, wall shear rate and convective back‐flow. Second, permeation flux was reduced with increasing fluid viscosity. Flux improvements (linear vs. helical membranes) of up to 45% were observed for all value of the silica suspensions with and without PEG. The energy required to obtain these improvements, however, was considerable. Flux advantages of the helical design decreased and eventually disappeared as the viscosity of the solution increased up to 12 times that of water at 27°C. New mass‐transfer correlations for microfiltration of poly(ethylene) glycol solutions containing silica concentrations for laminar flow in a helical and a linear module were obtained with respect to the solution viscosity, for a silica particle concentration of 0.1 wt. %.

Domestic wastewater treatment by a submerged membrane bioreactor with gravitational filtration

This study examined practical performance of a submerged membrane bioreactor with gravitational filtration, using a pilot-scale plant (volume of the bioreactor: 3.12 m 3) and raw domestic wastewater. Treated water was filtered through flat microfiltration membrane modules (polyethylene; pore size 0.4 μm) by the pressure head of bulk solution. A combined aerobic/anaerobic (single-sludge) system was used to enhance nitrogen removal. Operation was continued for 491 days. From the 267th to the 324th day of operation, seasonal inflow fluctuation was simulated by increasing inflow by 1.5- to 3-fold. The obtained results were summarized in the following four points. (1) Membrane filtration was able to be continued for the first 371 days without membrane washing and was still stable after the washing. (2) Average removal ratios of BOD, TOC, SS, total nitrogen, total phosphorous and coliform bacteria were 99, 93, 100, 79, 74% and 6-log units, respectively. (3) Experiments on simulated inflow fluctuation showed that the system could cope with a short-term fluctuation of inflow (up to threefold) without deteriorating filtration performances significantly. (4) Average power consumption by the experimental plant was 2.4 kWh per 1 m 3 of treated water.

Continuous anaerobic treatment of wastewater from a kraft pulp mill

A pilot-scale study of the thermophilic anaerobic digestion of high-strength wastewater (evaporator condensate, EC) discharged from a kraft pulp production process was performed. The system consisted of a microfiltration (MF) membrane module for oily substances removal, a stripping system using evolved gas from the digester for sulfur compounds removal, an anaerobic fixed-bed bioreactor for methane fermentation, and an ultrafiltration (UF) membrane module for retention of a high density of bacterial cells. The bioreactor had a fixed-bed with an effective volume of 5 m 3 packed with pumice stone. In a continuous run with only the MF membrane module for oily substances removal, the digester efficiency declined because of methanogenic inhibition by sulfur compounds. After fitting of the stripping system which used evolved gas from the digester, the inhibitive sulfur compounds in the EC were removed more than 80%, and high-loading and high-efficiency operation could be attained. The BOD loading and BOD removal of 35.5 kg BOD/m 3/d and 93%, respectively were attained. By anaerobic treatment of the evaporator condensate waste before the conventional aerobic activated sludge method, the total costs would be reduced to ¥3.31/m 3 wastewater compared with ¥4.53/m 3-wastewater by the aerobic activated sludge method only. The stability of digester performance against interruption by feed stoppage was also examined.